diff --git a/addons/snailmail/models/snailmail_letter.py b/addons/snailmail/models/snailmail_letter.py
index 53267c36538..10ec8424dd9 100644
--- a/addons/snailmail/models/snailmail_letter.py
+++ b/addons/snailmail/models/snailmail_letter.py
@@ -27,6 +27,7 @@ ERROR_CODES = [
     'NO_PRICE_AVAILABLE',
     'FORMAT_ERROR',
     'UNKNOWN_ERROR',
+    'ATTACHMENT_ERROR',
 ]